Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!floyd!harpo!seismo!hao!hplabs!sri-unix!Donald.Schmitz@CMU-RI-ARM
From: Donald.Schmitz%CMU-RI-ARM@sri-unix.UUCP
Newsgroups: net.sf-lovers
Subject: Re:Re:FTL
Message-ID: <317@sri-arpa.UUCP>
Date: Tue, 27-Mar-84 09:42:36 EST
Article-I.D.: sri-arpa.317
Posted: Tue Mar 27 09:42:36 1984
Date-Received: Fri, 30-Mar-84 03:27:01 EST
Lines: 23

Re the post by Michael Cooley in which he gives the example of two photons
approaching each other and claims the distance between them shrinks at speed
2c.  This seems like an example used to explain relativity that I've read
somewhere before, and the results are not exactly what are expected, as
what happens depends on the point of view. If viewed from a coordinate
system attached to either photon, the other appears to be
approaching at a speed just under c.  If viewed from a coordinate system
attached to say the point of collision of the two photons, the distance
between the two is shrinking at speed 2c, however this does not imply that
any physical object or information is traveling at speed greater than c.

If I've gotten any of the details wrong here (I'm working completely from
memory and can remember the text) please let me know.  Also, regarding the
question of one telepath traveling at relativistic speeds compared to the
other, Heinlein wrote a story based on just such a premise many years back
(one of his juvenile books I read in about 8th grade), with exactly what was
described happening.  The telepaths, taken along on the first star trip for
communication, had to concentrate on one idea for hours so that their earth
bound receptors could catch what they were sending, and had to use hypnosis
to pay attention to the return transmission long enough to understand it
(although transmission time was instantaneous).  

Don